The invention relates to fuel cells and, more particularly, to electrolyte-supported solid oxide fuel cells.
Direct conversion of chemical energy into electric energy, through use of fuel cells, is an important area of energy conversion technology. Among various types of fuel cells, the solid oxide fuel cell (SOFC) is of particular interest because operation of such fuel cells at high temperature allows direct use of natural gas as a fuel.
Fuel cells, including solid oxide fuel cells, have an electrolyte positioned between an anode and a cathode, and such a structure generates electric energy from fuel and oxidant as desired. In an electrolyte-supported SOFC, the electrolyte is the structure providing the mechanical integrity to the cell and the electrodes are held together structurally by the electrolyte.
The layers of a solid oxide fuel cell, that is, the electrolyte, anode and cathode, are typically quite thin. Thin electrolyte-supported cells, however, are subject to cracking during handling, assembly and operation because they have poor mechanical strength. While very thin electrolyte-supported cells (thickness <50 μm) may exhibit some amount of overall flexibility, local constraints (as with seals or ends) or during assembly and handling procedures can cause electrolyte fracture due to the poor strain tolerance of the ceramic electrolyte.
In addition, in an electrolyte-supported cell, electrodes are disposed and supported on the electrolyte, and these electrodes are also subject to cracking during operation.
Still further, strip-cell configuration involves positioning of via holes through the electrolyte so that communication can be established between adjacent elements of the assembly. These via holes can also experience cracking during operation.
Although these problems might dictate the use of a thicker electrolyte, this approach causes problems since the electrolyte thickness should be as small as possible in order to avoid high resistance to ion migration during electrochemical operation. The other option to decrease the resistance to ion migration is increasing the operating temperature which becomes impractical with metallic interconnects and current collectors.
Based upon the foregoing, it is clear that the need remains for improved electrolyte-supported solid oxide fuel cell structures.
It is therefore the primary object of the present invention to provide such structures.
Other objects and advantages of the present invention will appear hereinbelow.